The present invention relates to the Ocean Thermal Energy Conversion (herein referred as “OTEC”) system and more particularly to a design of a platform for an OTEC plant that integrates the distribution and collecting systems for the cold and surface waters with the condensers and evaporators.
OTEC systems are energy producing systems that exploit the temperature difference between warm surface waters in tropical seas and the cold waters in deeper ocean strata. In a conventional Closed Cycle OTEC, a working fluid is pumped by a pump into an evaporator, where heat from warm water is transferred to generate a working fluid vapor. The vapor moves a turbo-generator to generate electricity by conventional techniques. The spent vapor is condensed utilizing cold sea water from deep waters as a heat sink. Further details are provided in the description of FIG. 1. Additional information about the OTEC technology can be found in “Renewable Energy from the Ocean—A Guide to OTEC” by Avery and Wu—Oxford University Press—1994.
Typically an OTEC system would include a plant mounted on a platform, a ship or barge; a large diameter cold water pipe extending about 1,000 m below the surface; one or several turbo-generators, and; a plurality of heat exchangers (herein referred to as “HXs” when referring to a plurality of elements or as “HX” when referring to only one) used as evaporators, heaters and condensers. Water temperature at depths of about 1,000 m is about 4° C., while surface water in the tropics is about 25-28° C. Although an OTEC system is conceptually rather simple, the energy available from such small temperature difference is little, requiring moving large quantities of both deep and surface water and very large equipments, which present a design challenge. As an illustration, to produce a meaningful amount of electricity, say 100 MW, would require a Cold Water Pipe (herein referred as “CWP”) of 15-20 m in diameter and 1,000 m long; will require moving approximately 300 m3/s of both cold and surface water; about 10 million sqft of heat transfer surface in HXs; and a design for a platform that will minimize the energy consumption of pumping both surface and cold water. Having to raise the cold and surface water 1 m above the sea level will consume about 6 MW. Utilizing large, standard tube and shell HX of about 10,000 sqft would require 1,000 units. Utilizing small diameter finned tubes would increase the transfer area 4-7 times, but will still require 140-250 units, with each HX having to be fed by a water pipe of 4 to 6 ft. in diameter. Control valves and even following standard practice of placing valves before and after the HX is not practical and would produce large parasitic losses. The water distribution system needs to be simplified.